Electrical Fuse Structure and Method of Formation

ABSTRACT

Various fuse structures are disclosed herein that exhibit improved performance, such as reduced electro-migration. An exemplary fuse structure includes an anode, a cathode, and a fuse link extending between the anode and the cathode. A plurality of anode contacts are coupled to the anode, and a plurality of cathode contacts are coupled to the cathode. The plurality of cathode contacts are arranged symmetrically with respect to a centerline of the fuse link.

This is a divisional application of U.S. patent application Ser. No.14/333,333, filed Jul. 16, 2014, which is a continuation-in-part of U.S.patent application Ser. No. 14/231,231, filed Mar. 31, 2014, which is acontinuation of U.S. patent application Ser. No. 12/771,768, filed Apr.30, 2010, now U.S. Pat. No. 8,686,536, which claims the benefit of U.S.Provisional Patent Application Ser. No. 61/256,792, filed Oct. 30, 2009,and U.S. Provisional Patent Application Ser. No. 61/308,588, filed Feb.26, 2010, the entire disclosure of each of which is incorporated hereinby reference in its entirety.

TECHNICAL FIELD

The disclosure relates generally to a fuse structure and method offorming the fuse structure and, more particularly, to an electrical fusein a semiconductor device and method of forming the electrical fuse.

BACKGROUND

In the semiconductor industry, fuse elements are widely used features inintegrated circuits for a variety of purposes, such as in memory repair,analog resistor trimming, and chip identification. For example, byreplacing defective memory cells on chips with redundant cells on thesame chips, memory manufacturing yields can be significantly increased.A fuse disconnected by a laser beam is referred to as a laser fuse, anda fuse disconnected by passing an electrical current, or blowing, isreferred to as an electrical fuse, or e-fuse. By selectively blowingfuses within an integrated circuit that has multiple potential uses, ageneric integrated circuit design may be economically manufactured andadapted to a variety of custom uses.

E-fuses may be incorporated in the design of integrated circuits,wherein the fuses are selectively blown, for example, by passing anelectrical current of a sufficient magnitude to cause electro-migrationor melting of a fuse link, thereby creating a more resistive path or anopen circuit. However, a contact to a cathode of a conventional fuse maycause problems when a large electrical current passes through the fuse.This contact is generally aligned with an axis of a fuse link andnearest to the fuse link and has a very small contact area. Because thecontact is nearest to and aligned with the fuse link, the resistancebetween the fuse link and the contact is much lower than any resistancebetween the fuse link and any other contacts in the cathode. This lowresistance may cause a large proportion of the electrical current toflow through the contact.

The larger electrical current flowing through the contact may causeelectro-migration of the metal in the contact to the fuse link. Theelectro-migration of the metal then may cause the fuse link to shortcircuit again when the large electrical current was intended to create amore resistive path or open circuit. This problem is increased after ahigh temperature storage (HTS) or bake process of the chip. Accordingly,there is a need in the art for a more robust fuse structure to overcomethe deficiencies of the prior art.

SUMMARY

In accordance with an embodiment, a fuse structure comprises an anode, acathode, a fuse link interposed between the anode and the cathode, andcathode connectors coupled to the cathode. The cathode connectors areeach equivalent to or larger than about two times a minimum feature sizeof a contact that couples to an active device.

In accordance with another embodiment, a fuse structure comprises ananode, a cathode with connectors coupled to the cathode, and a fuse linkcoupled between the cathode and the anode. A cross-section area of eachof the connectors is equal to or larger than a cross-section area of aconnector coupling an active device.

In accordance with a further embodiment, a fuse structure comprises acathode, a fuse link, an anode, a dielectric over the cathode, openingsin the dielectric over the cathode, and metal connectors disposed in theopenings. The fuse link is coupled between the cathode and the anode.The openings expose a portion of the cathode, and a cross-sectional areaparallel to a top surface of the cathode of each of the openings isgreater than a minimum feature size.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present embodiments, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is an electrical fuse structure in accordance with an embodiment;

FIG. 2 is an electrical fuse structure in accordance with anotherembodiment;

FIG. 3 is an electrical fuse structure in accordance with a furtherembodiment;

FIG. 4 is an electrical fuse structure in accordance with an additionalembodiment;

FIGS. 5A-F are an exemplary process to form an electrical fuse structurein accordance with an embodiment;

FIGS. 6A-F are an illustrative process to form an electrical fusestructure in accordance with a further embodiment;

FIG. 7 is an electrical fuse structure that includes cathode contactsarranged an equal distance from the center of a fuse link in accordancewith an embodiment;

FIG. 8 is an electrical fuse structure that includes cathode contactsarranged an equal distance from the center of a fuse link in accordancewith a further embodiment;

FIG. 9 is an electrical fuse structure that includes a cathode contactand an anode contact that are the same size in at least one dimension inaccordance with an embodiment;

FIG. 10 is an electrical fuse structure that includes a cathode contactand an anode contact that are the same size in at least one dimension inaccordance with a further embodiment;

FIG. 11 is an electrical fuse structure that includes a cathode contactwithin a region aligned with a fuse link in accordance with anembodiment; and

FIG. 12 is an electrical fuse structure that includes a cathode contactwithin a region aligned with a fuse link in accordance with a furtherembodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the present embodiments are discussed in detailbelow. It should be appreciated, however, that this disclosure providesmany applicable inventive concepts that can be embodied in a widevariety of specific contexts. The specific embodiments discussed aremerely illustrative of specific ways to make and use the invention, anddo not limit the scope of the invention.

Embodiments will be described with respect to an electrical fusestructure in a semiconductor chip. Other embodiments contemplateapplications where the use of an electrical fuse structure is desirable.

FIG. 1 depicts a fuse structure 10 comprising a cathode 12, a fuse link14, and an anode 16. The fuse structure 10 may be formed of a metal,such as copper or the like, or silicided polysilicon, such as nickelsilicide (NiSi), titanium silicide (TiSi₂), cobalt silicide (CoSi_(x)),platinum silicide (PtSi₂), or the like. Cathode 12 has a rectangularshaped top surface and has two contacts 18 coupled to the top surface.Anode 16 has a funnel shaped top surface and has contacts 20 coupled tothe top surface. The contacts 18 and 20 may comprise copper, tungsten,or metals of the like, and may also comprise a diffusion barrier layerlining the contacts 18 and 20 comprising, for example, TiN, TaN, or thelike. The fuse link 14 has a width (perpendicular to arrow 22) muchsmaller than the width of the cathode 12 and the anode 16. Although thedescription herein refers to contacts 18 and 20, these contacts may bevias and/or contacts.

Contacts 18 in the cathode 12 couple a larger surface area of the topsurface of the cathode 12 than contacts coupling active devices in otherportions of the chip, such as to a transistor gate, and the contacts 18do not align or intersect a longitudinal axis through the fuse link 14that is represented by the arrow 22. For example, dashed lines 26illustrate longitudinal axes along edges of the fuse link 14 that definean area in the cathode 12 to which no contacts couple.

As a further exemplary embodiment and to further illustrate theembodiment in FIG. 1, examples of dimensions will be described withrespect to a technology node of 32 nm, but the dimensions are notlimiting with regard to embodiments described herein. One of ordinaryskill in the art will appreciate that the dimensions may be variedaccording to different technology nodes. In an embodiment in a 32 nmtechnology node device, the contacts 20 in the anode 16 may be a contactor via, and may have a surface area width of about 40 nm and a length ofabout 40 nm. Thus, the area of contacts 20 may be square. The contacts20 are said to be of a minimum feature size, which corresponds to thetechnology node of the embodiment, such as for gate electrodes,contacts, or metal lines. For example, a contact size may have acritical dimension of between about 15 nm and about 40 nm, and a viasize may have a critical dimension of between about 20 nm and about 50nm, each for a technology node of 32 nm. Thus, the contacts 20 may beequal to or larger than about the minimum feature size of a contact thatcouples an active device in another portion of the chip, such as to atransistor gate, or further, may be between about one times to about twotimes the minimum feature size of a contact that couples an activedevice in another portion of the chip. Minimum feature sizes fordifferent technology nodes will have different critical dimensions.

The fuse link 14 may have a length of approximately 240 nm and a widthof between about 40 nm and about 60 nm. Thus, the fuse link 14 width maybe equivalent to or larger than about the minimum feature size of a gateelectrode, or further, may be between about one times and about twotimes the minimum feature size of a gate electrode. Alternatively, thefuse link 14 width may be equivalent to or larger than about the minimumfeature size of a width of a metal line, or further, may be betweenabout one times and about two times the minimum feature size of thewidth of the metal line. The contacts 18 in the cathode 12 may have asurface area width of about 120 nm and a length of about 120 nm. Thus,the area of contacts 18 may be square, and may be equal to or greaterthan about two times the minimum feature size of a contact that couplesan active device in another portion of the chip, or further, may rangefrom about two times to about four times the minimum feature size of acontact coupling an active device. These dimensions may be variedaccording to, for example, a different technology node or according todifferent desires and needs of a design.

The arrow 22 also represents the direction of the flow of electrons whenan electrical current is applied to the fuse structure 10. Thus, as isreadily apparent to a person having ordinary skill in the art, thecontacts 18 are equidistant from the fuse link 14 such that theresistances between the fuse link 14 and each of the contacts 18 mayalso be equal. The equal resistances may cause the current flowingthrough the fuse link 14 to be substantially evenly proportioned betweeneach contact 18. This may reduce a large current that may be isolated toa single contact of the prior art. Further, the contact areas of thecontacts 18 are substantially larger such that the current density in asingle contact 18 may be reduced when an electrical current is appliedto the fuse structure. The reduced magnitude of current and currentdensity flowing through any single contact 18 generally causes the fusestructure to have a more robust electro-migration capability such thatthe metal in or above the contacts 18 are generally less likely tomigrate to the fuse link 14 and short the fuse structure 10.

FIGS. 2 through 4 illustrate further embodiments. The embodiments inFIGS. 2 through 4 may be desirable when more contacts are needed forredundancy. FIG. 2 illustrates a fuse structure 30 comprising a cathode32. The cathode 32 comprises a one-by-four array of inner and outercontacts 34 a and 34 b, respectively, which are referred to collectivelyas the contacts 34, which may also be vias. The contacts 34 again arenot aligned with the fuse link 14 but are offset from the longitudinalaxis of the fuse link. The inner contacts 34 a are equidistant from alongitudinal axis of the fuse link 14, or from the area defined bydashed lines 26, and outer contacts 34 b are equidistant from thelongitudinal axis. The contacts 34 have a contact surface area that islarger. The contacts 34 may each be approximately 120 nm in length andabout 60 nm in width, although other dimensions may be used.

FIG. 3 illustrates a fuse structure 40 comprising a cathode 42. Thecathode 42 comprises a two-by-two array of contacts 44 (which arefurther designated as contacts 44 a and contacts 44 b), which may alsobe vias. The contacts 44 again are not aligned with the fuse link 14 andhave a relatively larger contact surface area. The two contacts 44 amore proximate the fuse link 14 are equidistant from a longitudinal axisof the fuse link 14, and the two contacts 44 b furthest from the fuselink 14 are equidistant from the longitudinal axis. The contacts mayeach be approximately 60 nm in length and about 120 nm in width, butother dimensions are contemplated within scopes of this embodiment.

FIG. 4 illustrates a fuse structure 50 comprising a cathode 52. Thecathode 52 comprises a two-by-four array of contacts 54, which may alsobe vias. The contacts 54 are likewise not aligned with the fuse link 14and have a relatively larger contact surface area. Pairs ofcorresponding contacts 54 are equidistant from a longitudinal axis ofthe fuse link 14. Contacts 54 are symmetrically arranged on opposingsides of the longitudinal axis of the fuse link 14. The contacts 54 mayeach be approximately 60 nm in length and about 60 nm in width, but thedimensions may be varied.

FIGS. 5A through 5F illustrate an exemplary method to form a fusestructure in accordance with embodiments. These figures illustrate across-section of a cathode of the fuse structure, for example, thecathode 12 in FIG. 1 along line A-A. In FIG. 5A, a semiconductorsubstrate 102 is provided, such as silicon, silicon-germanium, or thelike. A recess is etched in the semiconductor substrate 102, and adielectric is formed in the recess to create a shallow trench isolation(STI) 104. The dielectric may be formed by oxidizing the semiconductorsubstrate 102, by depositing the dielectric over the semiconductorsubstrate 102, or similar techniques.

In FIG. 5B, a metal or polysilicon layer 106 is formed over thesemiconductor substrate 102, such as by a blanket deposition. If metalis used, the metal layer 106 may comprise copper or the like. Aphotoresist 108 is then formed above the metal or polysilicon layer 106that is above the STI 104. The top surface of the photoresist 108 ispatterned similar to the top surface illustrated in FIGS. 1 through 4.The dashed lines in the photoresist 108 indicate the width of a fuselink in the subsequent fuse structure.

In FIG. 5C, an etch process is carried out such that the pattern of thephotoresist 108 is imposed on the metal or polysilicon layer 106. Thedashed lines in the metal or polysilicon layer 106 show the width of afuse link coupled to the cathode. If polysilicon is used in the metal orpolysilicon layer 106, the polysilicon then may be silicided bydepositing a metal, such as titanium, cobalt, nickel, platinum, or thelike, and annealing the structure to create titanium silicide, cobaltsilicide, nickel silicide, platinum silicide, or other similarsilicides. Then, a dielectric layer 110, such as an interlayerdielectric (ILD), is deposited over the semiconductor substrate 102. Aphotoresist 112 is deposited over the dielectric layer 110 and patternedto expose portions of the dielectric layer 110 over the remaining metalor polysilicon layer 106 through openings 114.

In FIG. 5D, an etch process is carried out to impose the pattern ofopenings 114 into the dielectric layer 110 to form openings 116. Anotherphotoresist 118 is then formed over the dielectric layer 110 with anopening 120 patterned therein. An isotropic etch is then carried out toform an opening in the dielectric layer 110 so that contactssubsequently formed in openings 116 are coupled together. This processthus describes the use of a dual damascene process. However, embodimentsare not limited to this process, and a person having ordinary skill inthe art will readily understand the efficacy of a single damasceneprocess or other like processes.

In FIG. 5E, a conformal diffusion barrier layer 122 is deposited overthe structure and a metal 124 is deposited over the diffusion barrierlayer 122. The diffusion barrier layer 122 may be any known barrierlayer, such as titanium nitride, tantalum nitride, or the like. Themetal 124 may be copper, tungsten, or the like.

In FIG. 5F, excess metal 124 is removed, and diffusion barrier layer 122over the dielectric layer 110 that is not within any of the formedopenings is removed, such as by a chemical mechanical polish (CMP).Accordingly, contacts 126 are formed coupling the metal or polysiliconlayer 106 that is the cathode, and line 128 couples the contacts 126together and forms an area to which vias in subsequent intermetaldielectric (IMD) layers may be coupled. The contacts 126 thus formedhave a larger contact area and are not aligned with any fuse link, asindicated by the dashed lines. This process may result in the layout ofthe fuse structure 10 as illustrated in FIG. 1, though it is noted thatline 128 is not depicted in FIG. 1. A person having ordinary skill inthe art will readily understand any needed modifications to this processto form other embodiments, such as those in FIGS. 2 through 4.

FIGS. 6A through 6F illustrate another exemplary method to form a fusestructure in accordance with embodiments. These figures illustrate across-section of a cathode of the fuse structure, for example, thecathode 12 in FIG. 1 along line A-A. In FIG. 6A, a first dielectriclayer 202 is provided, such as silicon dioxide, silicon nitride, siliconoxynitride, or the like. The first dielectric layer 202 may be formedabove a semiconductor substrate, such as part of an interlayerdielectric (ILD) or intermetal dielectric (IMD) layer in a semiconductorchip. A photoresist 204 is patterned over the first dielectric layer 202with opening 206 therein. The opening 206 is patterned similar to thetop surface illustrated in FIGS. 1 through 4. The vertical dashed linesin the photoresist 204 indicate the width of a fuse link in thesubsequent fuse structure, and the horizontal dashed lines show the topsurface of the photoresist 204 around other areas of opening 206.

In FIG. 6B, the first dielectric layer 202 is etched such that opening206 is imposed into the dielectric layer 202. A metal or polysiliconlayer 208 is formed over the first dielectric layer 202, such as by ablanket deposition. If metal is used, the metal layer 208 may comprisecopper or the like. Any excess metal or polysilicon is then removed,such as by a chemical mechanical polish (CMP). If polysilicon is used asa polysilicon layer 208, a metal, such as titanium, cobalt, nickel,platinum, or the like, may be deposited over the polysilicon andannealed to form a silicide, such as titanium silicide, cobalt silicide,nickel silicide, platinum silicide, or other similar silicides.

In FIG. 6C, a second dielectric layer 210 is deposited over the firstdielectric layer 202 and the metal or polysilicon 208. The seconddielectric layer 210 may be a subsequent ILD or IMD layer. A photoresist212 is deposited over the second dielectric layer 210 and patterned toexpose portions of the dielectric layer 210 over the remaining metal orpolysilicon layer 208 through openings 214.

In FIG. 6D, an etch process is carried out to impose the pattern ofopenings 214 into the second dielectric layer 210 to form openings 218.Another photoresist 216 is then formed over the second dielectric layer210 with an opening 220 patterned therein. An isotropic etch is thencarried out to form an opening in the second dielectric layer 210 sothat contacts subsequently formed in openings 218 are coupled together.This process thus describes the use of a dual damascene process.However, embodiments are not limited to this process, and a personhaving ordinary skill in the art will readily understand the efficacy ofa single damascene process or other like processes.

In FIG. 6E, a conformal diffusion barrier layer 222 is deposited overthe structure and a metal 224 is deposited over the diffusion barrierlayer 222. The diffusion barrier layer 222 may be any known barrierlayer, such as titanium nitride, tantalum nitride, or the like. Themetal 224 may be copper, tungsten, or the like.

In FIG. 6F, excess metal 224 is removed, and diffusion barrier layer 222over the second dielectric layer 210 that is not within any of theformed openings is removed, such as by a chemical mechanical polish(CMP). Accordingly, vias 226 are formed coupled to the metal orpolysilicon layer 206 that is the cathode, and line 228 couples the vias226 together and forms an area to which vias in subsequent IMD layersmay be coupled. The vias 226 thus formed have a larger contact area andare not aligned with any fuse link, as indicated by the dashed lines.This process may result in the layout of the fuse structure 10illustrated in FIG. 1, though it is noted that line 228 is not depictedin FIG. 1. A person having ordinary skill in the art will readilyunderstand any needed modifications to this process to form otherembodiments, such as those in FIGS. 2 through 4.

Further exemplary embodiments that apply the principles of the presentdisclosure are disclosed with respect to FIGS. 7-12. The fuse structuresillustrated therein apply these principles to provide reducedelectro-migration and greater reliability.

Referring first to FIG. 7, the illustrated fuse structure 300 is similarin some regards to fuse structure 10 of FIG. 1 in that the cathodecontacts are spaced substantially equidistant from the center of thefuse link 14. By arranging the contacts at an equal distance, theresistive paths from the contacts to the fuse link 14 are madesubstantially similar, which equalizes the current flowing through thecathode contacts. As described above, equalizing the current through thecathode contacts reduces the chance that a disproportionately largecurrent through a single contact will cause electro-migration ofconductive material to recouple a severed fuse link 14.

The exemplary fuse structure 300 includes a conductive material such asa metal (e.g., copper), polysilicon, a silicided polysilicon (e.g.,nickel silicide, titanium silicide, cobalt silicide, platinum silicide,etc.), other suitable conductors, and/or combinations thereof. Theconductive material has a cathode 302 defined at one end and an anode 16defined at an opposite end. A fuse link 14 extends between andelectrically couples the cathode 302 and the anode 16 when in an unblownstate. The fuse link 14 and the anode 16 may be substantially similar tothe fuse link 14 and anode 16 described with reference to FIGS. 1-4 andwill only be described briefly. In the illustrated embodiment, the fuselink 14 includes a segment of the conductive material having arectangular top surface. The width of the fuse link 14 (perpendicular toarrow 22 indicating the direction of current flow) may be smaller thanthe width of the cathode 302 and the anode 16 so that current flowingthrough the structure is concentrated in the fuse link 14. When aprogramming voltage is applied to the fuse structure 300, the currentflowing through and concentrated by the fuse link 14 damages it,producing a discontinuity between the cathode 302 and the anode 16. Inthe example, the anode 16 includes a first region with a funnel-shapedtop surface of the conductive material defined by a tapered portionphysically contacting the fuse link 14 and a second region with arectangular-shaped top surface opposite the fuse link 14. The fusestructure 300 includes one or more anode contacts 20 electricallycoupled to the top surface of the anode 16.

Turning to the cathode 302, in the illustrated embodiment, the cathode302 includes a region of the conductive material with a rectangular topsurface. One or more cathode contacts 304 are electrically andphysically coupled to the top surface. Electrical current flowingthrough the fuse structure 300 flows through the cathode contacts 304,through the cathode 302, through the fuse link 14 in the direction ofarrow 22, and to the anode 16. Because the portion of the currentflowing through a particular cathode contact 304 depends on theassociated resistance, and because resistance is proportional todistance, the cathode contacts 304 are arranged an equal distance fromthe center of the fuse link 14. More specifically, the cathode contacts304 are arranged such that a center point of each contact issubstantially equidistant from the center point 306 of the boundarybetween the fuse link 14 and the cathode 302. In FIG. 7, the boundarybetween the fuse link 14 and the cathode 302 is shown as a dashed line.The dashed line is for reference as, in the unprogrammed state, theconductive material of the cathode 302 may extend continuously into theconductive material of the fuse link 14.

The embodiment of FIG. 7 includes three cathode contacts 304 spaced atan equal distance from the center point 306, although this number ismerely exemplary. In further embodiments, the fuse structure 300includes four or more cathode contacts 304 arranged in this manner.

In order to further reduce electro-migration, the contact areas of thecathode contacts 304 in the current embodiment are larger than that ofthe anode contacts 20. This reduces the current density in the cathodecontacts 304 and may cause the fuse structure 300 to have a more robustelectro-migration capability. In other words, the metal in or above thecontacts 304 is generally less likely to migrate to the fuse link 14 andshort the fuse structure 300. In that regard, the cathode contacts 304are larger than the anode contacts 20 along both a first direction(indicated by axis 308) and a second direction (indicated by axis 310)perpendicular to the first direction. In an example, the cathodecontacts 304 may each have a cross-sectional area between about two andabout four times the cross-sectional area of an anode contact 20. Incontrast, the anode contacts 20 may be between about one times and abouttwo times the minimum contact feature size in the example.

However because of the complexity of fabricating minute devices, manyprocess parameters are optimized for particular device sizes.Accordingly, in some fabrication processes, steps such as etching aretuned for a single contact size or aspect ratio. In one example, afabrication technique is configured to produce a substantially squarecontact 15 nm wide (along axis 308) and 15 nm long (along axis 310). Dueto etch biasing and other real-world effects, a fabrication processoptimized to reliably form contacts of a first size may exhibit yieldproblems when forming contacts of a second size, even if the second sizeis larger than the first.

Referring to FIG. 8, a fuse structure 400 is disclosed that includescathode contacts configured to be substantially the same size as theanode contacts in at least one dimension in order to reduce thesefabrication irregularities and others. Similar to the fuse structure 300of FIG. 7, the cathode contacts are spaced substantially equidistantfrom the center of the fuse link 14. By arranging the contacts at anequal distance, the resistive paths from the contacts to the fuse link14 are substantially similar, and the likelihood of a disproportionatelylarge current through a single contact and the associatedelectro-migration is reduced.

In many aspects, the fuse structure 400 of FIG. 8 is substantiallysimilar to the fuse structure 300 of FIG. 7. For example, fuse structure400 includes a conductive material with a cathode 402 defined at oneend, an anode 16 defined at an opposite end, and a fuse link 14extending between and electrically coupling the cathode 402 and theanode 16 when in an unblown state. The fuse link 14 and the anode 16 maybe substantially similar to the fuse link 14 and anode 16 described withreference to FIG. 7. For example, in the illustrated embodiment, thefuse link 14 includes a segment of the conductive material having arectangular top surface with a width (perpendicular to arrow 22indicating the direction of current flow) that is smaller than the widthof the cathode 402 and the anode 16. In the example, the anode 16includes a first region with a funnel-shaped top surface of theconductive material defined by a tapered portion physically contactingthe fuse link 14 and a second region with a rectangular-shaped topsurface opposite the fuse link 14. The fuse structure 400 includes oneor more anode contacts 20 electrically coupled to the top surface of theanode 16.

With respect to the cathode 402, it includes a region of the conductivematerial having a substantially rectangular top surface and one or morecathode contacts 404 electrically and physically coupled to the topsurface. The cathode contacts 404 are arranged so that a center point ofeach contact is substantially equidistant from a center point of theboundary between the fuse link 14 and the cathode 402 (indicated bymarker 406). In the illustrated embodiment, the cathode 402 includesthree cathode contacts 404 positioned at this spacing, although thisnumber is merely exemplary. In further embodiments, the cathode 402includes other numbers of cathode contacts 404. Because resistance isproportional to distance and because current through a cathode contact404 depends on the associated resistance, the equidistant spacingreduces the chance of a particular cathode contact 404 experiencing adisproportionate current load.

In various embodiments, the cathode contacts 404 are the same size asthe anode contacts 20 in one or more directions, (e.g., along axis 408and/or axis 410), particularly where the fabrication environment hasbeen optimized for a size of an anode contact 20. In one suchembodiment, the cathode contacts 404 have the same width as the anodecontacts 20 along axis 408 and a different length from the anodecontacts 20 along axis 410. In a further such embodiment, the cathodecontacts 404 have the same length as the anode contacts 20 along axis410 and a different width from the anode contacts 20 along axis 408. Inyet a further such embodiment, the cathode contacts 404 have the samewidth as the anode contacts 20 along axis 408 and the same length as theanode contacts 20 along axis 410. By selecting from these embodiments, adesigner may choose a cathode contact 404 configuration that provides anoptimal balance of current density, electro-migration resistance, andease of fabrication.

Referring to FIG. 9, an alternate fuse structure 500 is disclosed thatincludes cathode contacts that are the same size as the anode contactsin at least one dimension in order to reduce fabrication irregularities.Similar to the fuse structures of FIGS. 1-4, the cathode contacts arespaced away from a contact free region as wide as the fuse link 14 andextending completely through the cathode.

In many aspects, the fuse structure 500 of FIG. 9 is substantiallysimilar to the fuse structures of FIGS. 1-4. For example, fuse structure500 includes a conductive material with a cathode 502 defined at oneend, an anode 16 defined at an opposite end, and a fuse link 14extending between and electrically coupling the cathode 502 and theanode 16 when in an unblown state. The fuse link 14 and the anode 16 maybe substantially similar to the fuse link 14 and anode 16 described withreference to FIGS. 1-4. For example, in the illustrated embodiment, thefuse link 14 includes a segment of the conductive material having arectangular top surface with a width (perpendicular to arrow 22indicating the direction of current flow) that is smaller than the widthof the cathode 502 and the anode 16. In the example, the anode 16includes a first region with a funnel-shaped top surface of theconductive material defined by a tapered portion physically contactingthe fuse link 14 and a second region with a rectangular-shaped topsurface opposite the fuse link 14. The fuse structure 500 includes oneor more anode contacts 20 electrically coupled to the top surface of theanode 16.

With respect to the cathode 502, it includes a region of the conductivematerial having a substantially rectangular top surface, and one or morecathode contacts 504 electrically and physically coupled to the topsurface. An exemplary cathode 502 comprises a one-by-four array ofcathode contacts 504, although this number of cathode contacts 504 ismerely exemplary. The cathode contacts 504 are positioned outside aregion of the cathode 502 defined by longitudinal axes along the edgesof the fuse link 14 (represented by dashed lines 26) and extendingcompletely through the cathode region 502. In this way, the contacts 504are not aligned with the fuse link 14 but instead are offset from thelongitudinal axis of the fuse link. The cathode contacts 504 may bearranged to be symmetrical with respect to the centerline (representedby dashed line 506) of the fuse link 14.

In various embodiments, the cathode contacts 504 are the same size asthe anode contacts 20 in one or more directions, (e.g., along axis 508and/or axis 510), particularly where the fabrication environment hasbeen optimized for a size of an anode contact 20. In the illustratedembodiment, the cathode contacts 504 have the same width as the anodecontacts 20 along axis 508 and a different length from the anodecontacts 20 along axis 510. For example, the cathode contacts 504 may belarger than the anode contacts 20 along axis 510 to reduce currentdensity and thereby reduce electro-migration. In various such examples,the cathode contacts 504 each have a cross-sectional area between abouttwo and about four times the cross-sectional area of an anode contact20. In another such embodiment, the cathode contacts 504 have the samelength as the anode contacts 20 along axis 510 and a different widthfrom the anode contacts 20 along axis 508. In a further such embodiment,the cathode contacts 504 have the same width as the anode contacts 20along axis 508 and the same length as the anode contacts 20 along axis510. By selecting from these embodiments, a designer may choose acathode contact 504 configuration that provides an optimal balance ofcurrent density, electro-migration resistance, and ease of fabrication.

Referring to FIG. 10, yet another fuse structure 600 is disclosed thatincludes cathode contacts that are the same size as the anode contactsin at least one dimension in order to reduce fabrication irregularities.In many aspects, the fuse structure 600 of FIG. 10 is substantiallysimilar to the fuse structures of FIGS. 1-4. For example, fuse structure600 includes a conductive material with a cathode 602 defined at oneend, an anode 16 defined at an opposite end, and a fuse link 14extending between and electrically coupling the cathode 602 and theanode 16 when in an unblown state. The fuse link 14 and the anode 16 maybe substantially similar to the fuse link 14 and anode 16 described withreference to FIGS. 1-4. For example, in the illustrated embodiment, thefuse link 14 includes a segment of the conductive material having arectangular top surface with a width (perpendicular to arrow 22indicating the direction of current flow) that is smaller than the widthof the cathode 602 and the anode 16. In the example, the anode 16includes a first region with a funnel-shaped top surface of theconductive material defined by a tapered portion physically contactingthe fuse link 14 and a second region with a rectangular-shaped topsurface opposite the fuse link 14. The fuse structure 600 includes oneor more anode contacts 20 electrically coupled to the top surface of theanode 16.

With respect to the cathode 602, it includes a region of the conductivematerial having a substantially rectangular top surface and one or morecathode contacts 604 electrically and physically coupled to the topsurface. An exemplary cathode 602 comprises a one-by-three array ofcathode contacts 604, although this number of cathode contacts 604 ismerely exemplary. In order to arrange an odd number of cathode contacts604 symmetrically with respect to the centerline (represented by dashedline 606) of the fuse link 14, one or more of the cathode contacts 604are positioned within the region of the cathode 602 defined bylongitudinal axes along the edges of the fuse link 14 (represented bydashed lines 26) that extends completely through the cathode region 602.

In various embodiments, the cathode contacts 604 are the same size asthe anode contacts 20 in one or more directions, (e.g., along axis 608and/or axis 610), particularly where the fabrication environment hasbeen optimized for a size of an anode contact 20. In the illustratedembodiment, the cathode contacts 604 have the same width as the anodecontacts 20 along axis 608 and a different length from the anodecontacts 20 along axis 610. For example, the cathode contacts 604 may belarger than the anode contacts 20 along axis 610 to reduce currentdensity and thereby reduce electro-migration. In various such examples,the cathode contacts 604 each have a cross-sectional area between abouttwo and about four times the cross-sectional area of an anode contact20. In another such embodiment, the cathode contacts 604 have the samelength as the anode contacts 20 along axis 610 and a different widthfrom the anode contacts 20 along axis 608. In a further such embodiment,the cathode contacts 604 have the same width as the anode contacts 20along axis 608 and the same length as the anode contacts 20 along axis610. By selecting from these embodiments, a designer may choose acathode contact 604 configuration that provides an optimal balance ofcurrent density, electro-migration resistance, and ease of fabrication.

Referring to FIG. 11, a fuse structure 700 is disclosed that includes acathode contact within the region aligned with the fuse link. Thecathode contact extends beyond the region on two sides, and the enlargedcathode contact provides increased surface area for reduced currentdensity and electro-migration. By extending beyond the width of the fuselink, the current density in the cathode contact may be lower than thatof the fuse link. In some such embodiments, the cathode contact is thesame size as the anode contacts in at least one dimension in order toreduce fabrication irregularities.

In many aspects, the fuse structure 700 of FIG. 11 is substantiallysimilar to the fuse structures of FIGS. 1-4. For example, fuse structure700 includes a conductive material with a cathode 702 defined at oneend, an anode 16 defined at an opposite end, and a fuse link 14extending between and electrically coupling the cathode 702 and theanode 16 when in an unblown state. The fuse link 14 and the anode 16 maybe substantially similar to the fuse link 14 and anode 16 described withreference to FIGS. 1-4. For example, in the illustrated embodiment, thefuse link 14 includes a segment of the conductive material having arectangular top surface with a width (perpendicular to arrow 22indicating the direction of current flow) that is smaller than the widthof the cathode 702 and the anode 16. In the example, the anode 16includes a first region with a funnel-shaped top surface of theconductive material defined by a tapered portion physically contactingthe fuse link 14 and a second region with a rectangular-shaped topsurface opposite the fuse link 14. The fuse structure 700 includes oneor more anode contacts 20 electrically coupled to the top surface of theanode 16.

With respect to the cathode 702, it includes a region of the conductivematerial having a substantially rectangular top surface and one or morecathode contacts 704 electrically and physically coupled to the topsurface. In the illustrated embodiment, the cathode 702 comprises a onesingle cathode contact 704, although this number is merely exemplary.The cathode contact 704 is positioned within the region of the cathode702 defined by longitudinal axes along the edges of the fuse link 14(represented by dashed lines 26) that extends through the cathode region702, and in some examples, the contact 704 extends beyond the region ontwo opposing sides.

In various embodiments, the cathode contact 704 is the same size as theanode contacts 20 in one or more directions, (e.g., along axis 708and/or axis 710), particularly where the fabrication environment hasbeen optimized for a size of the anode contact 20. In the illustratedembodiment, the cathode contact 704 has the same length as the anodecontacts 20 along axis 710 and a different width from the anode contacts20 along axis 708. For example, the cathode contact may be larger thanthe anode contacts 20 along axis 708 to reduce current density andthereby reduce electro-migration. In various such examples, the cathodecontact 704 has a cross-sectional area between about two and about fourtimes the cross-sectional area of an anode contact 20. In another suchembodiment, the cathode contact 704 has the same width as the anodecontacts 20 along axis 708 and a different length from the anodecontacts 20 along axis 708. In a further such embodiment, the cathodecontact 704 has the same width as the anode contacts 20 along axis 708and the same length as the anode contacts 20 along axis 710. Byselecting from these embodiments, a designer may choose a cathodecontact 504 configuration that provides an optimal balance of currentdensity, electro-migration resistance, and ease of fabrication.

The cathode contact 704 may be spaced any suitable distance from theboundary between the cathode 702 and the fuse link as indicated byreference arrow 712. Generally, positioning the cathode contact 704further from the boundary may increase electro-migration resistance butmay also increase programming voltage or programming current. FIG. 12illustrates a particular example where the cathode contact 804 isaligned with or even extends beyond the boundary. FIG. 12 is anillustration of a fuse structure 800 that is substantially similar inmany regard to fuse structure 700 of FIG. 11. For example, fusestructure 800 includes a cathode 802, an anode 16, anode contacts 20,and a fuse link 14, each substantially similar to those of FIG. 11.

The fuse structure 800 also includes a cathode contact 804 electricallyand physically coupled to the top surface of the cathode 802. Thecathode contact 804 is positioned within the region of the cathode 802defined by longitudinal axes along the edges of the fuse link 14(represented by dashed lines 26) that extends through the cathode region802, and in some examples, the contact 804 extends beyond the region ontwo opposing sides. In contrast to previous examples, the contact 804also extends to the boundary between the cathode 802 and the fuse link14, and in some embodiments, is electrically and physically coupled to atop surface of the fuse link 14. In various embodiments, the cathodecontact 804 is the same size as the anode contacts 20 in one or moredirections, (e.g., along axis 808 and/or axis 810), particularly wherethe fabrication environment has been optimized for a size of the anodecontact 20.

Thus, a fuse structure with improved electro-migration resistance and amethod of forming the fuse structure are provided. In some embodiments,the electrical device includes an anode disposed at a first end and ananode connector coupled to the anode. The electrical device includes acathode disposed at a second end and a plurality of cathode connectorscoupled to the cathode. The electrical device also includes a fuse linkextending between and contacting the anode and the cathode. A boundarybetween the fuse link and the cathode has a center point, and eachconnector of the plurality of cathode connectors has a center point thatis an equal distance from the center point of the boundary between thefuse link and the cathode. In some such embodiments, each connector ofthe plurality of cathode connectors is a different size than the anodeconnector, whereas in some such embodiments, each connector of theplurality of cathode connectors is substantially a same size as theanode connector along at least one axis.

In further embodiments, a fuse structure is provided that includes ananode, a cathode, and a segment contacting and electrically coupling theanode and the cathode. The cathode has a substantially rectangular topsurface and a plurality of cathode contacts disposed on the top surfaceof the cathode. A boundary of a top surface of the segment and the topsurface of the cathode has a center point defined thereupon, and eachcathode contact of the plurality of cathode contacts is spaced an equaldistance from the center point. In some such embodiments, the pluralityof cathode contacts includes at least three cathode contacts.

In yet further embodiments, a fuse structure is provided that includesan anode having an anode contact, a cathode having a cathode contact,and a fuse link extending between the anode and the cathode. The fuselink has a first edge extending along and defining a first plane and asecond edge extending along and defining a second plane, and the cathodeincludes a region extending from the first plane to the second plane andextending from the fuse link to an edge of the cathode opposite the fuselink. The cathode contact extends within the region of the cathode fromthe first plane to the second plane. In some such embodiments, thecathode contact extends beyond the first plane and the second planeoutside the region of the cathode.

Although these embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure, processes, machines, manufacture, compositions of matter,means, methods, or steps, presently existing or later to be developed,that perform substantially the same function or achieve substantiallythe same result as the corresponding embodiments described herein may beutilized according to the present invention. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

What is claimed is:
 1. A fuse structure comprising: an anode; a cathode;a fuse link extending between the anode and the cathode; a plurality ofanode contacts coupled to the anode; and a plurality of cathode contactscoupled to the cathode, wherein the plurality of cathode contacts arearranged symmetrically with respect to a centerline of the fuse link. 2.The fuse structure of claim 1, wherein the cathode includes a centralregion defined by a first longitudinal axis and a second longitudinalaxis extending respectively from a first edge and a second edge of thefuse link, and further wherein none of the plurality of cathode contactsare disposed in the central region.
 3. The fuse structure of claim 1,wherein the cathode includes a central region defined by a firstlongitudinal axis and a second longitudinal axis extending respectivelyfrom a first edge and a second edge of the fuse link, and furtherwherein at least one of the plurality of cathode contacts is disposed inthe central region.
 4. The fuse structure of claim 1, wherein theplurality of anode contacts are arranged differently than the pluralityof cathode contacts.
 5. The fuse structure of claim 1, wherein a widthof the plurality of cathode contacts is substantially the same as awidth of the plurality of anode contacts.
 6. The fuse structure of claim1, wherein a length of the plurality of cathode contacts issubstantially the same as a length of the plurality of anode contacts.7. The fuse structure of claim 1, wherein a size of the plurality ofcathode contacts is substantially the same as a size of the plurality ofanode contacts.
 8. The fuse structure of claim 1, wherein each of theplurality of cathode contacts has a cross-sectional area between abouttwo times and about four times a cross-sectional area of at least one ofthe plurality of anode contacts.
 9. A fuse structure comprising: ananode; a cathode; a fuse link extending between the anode and thecathode, wherein the fuse link has a width defined between a first edgeand a second edge, and further wherein the first edge and the secondedge extend a length of the fuse link; wherein the cathode includes acentral region defined by a first longitudinal axis and a secondlongitudinal axis extending respectively from the first edge and thesecond edge of the fuse link, the first longitudinal axis and the secondlongitudinal axis extending a length of the cathode; a plurality ofanode contacts coupled to the anode; and a cathode contact coupled tothe cathode, wherein the cathode contact is disposed within the centralregion, and further wherein the cathode contact has a width that extendsbeyond the first longitudinal axis and the second longitudinal axis. 10.The fuse structure of claim 9, wherein the cathode contact is spacedaway from a boundary between the fuse link and the cathode.
 11. The fusestructure of claim 9, wherein the cathode contact is adjacent to aboundary between the fuse link and the cathode.
 12. The fuse structureof claim 9, wherein the width of the cathode contact is substantiallythe same as a width of the plurality of anode contacts.
 13. The fusestructure of claim 9, wherein a length of the cathode contact issubstantially the same as a length of the plurality of anode contacts.14. The fuse structure of claim 9, wherein the cathode contact has across-sectional area that is larger than a cross-sectional area of atleast one of the plurality of anode contacts.
 15. The fuse structure ofclaim 9, wherein the cathode is rectangular shaped and the anode isfunnel shaped.
 16. A fuse structure comprising: an anode; a cathode; afuse link extending between the anode and the cathode, wherein the fuselink has a width defined between a first edge and a second edge, andfurther wherein the first edge and the second edge extend a length ofthe fuse link; a plurality of cathode contacts coupled to the cathode,wherein the plurality of cathode contacts are arranged symmetricallywith respect to a centerline of the fuse link; and wherein the cathodeincludes a central region defined by a first longitudinal axis and asecond longitudinal axis extending respectively from the first edge andthe second edge of the fuse link, the first longitudinal axis and thesecond longitudinal axis extending a length of the cathode, and thecentral region being free of the plurality of cathode contacts.
 17. Thefuse structure of claim 16, wherein each of the plurality of cathodecontacts is offset from the first longitudinal axis or the secondlongitudinal axis.
 18. The fuse structure of claim 16, wherein theplurality of cathode contacts includes at least one cathode contact pairincluding a first cathode contact and a second cathode contact, whereinthe first cathode contact is offset from the first longitudinal axis andthe second cathode contact is offset from the second longitudinal axis.19. The fuse structure of claim 16, wherein the plurality of cathodecontacts is a one-by-four array of cathode contacts.
 20. The fusestructure of claim 16, further comprising at least one anode contactcoupled to the anode, wherein the cathode has a dimension that is thesame as a dimension of the at least one anode contact.